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TDMA Systems
Communications Transmission Analysis for the ESA OTS and EUTELSAT ECS Satellite Systems
Carried out the transmission analysis of the QPSK/TDMA systems for the OTS and ECS satellite communications systems during a two year period. This included :
  • Development of comprehensive computer simulation models of QPSK/TDMA transmission via non-linear earth station and satellite, including the effects of co-channel and adjacent-channel interference and adjacent-channel multipath.
  • Evaluation of the effects of burst-mode transmission on satellite TWTA amplifiers, including helix-cathode supply circuit impedance variations (and resulting am/pm conversion variations) as a function of TDMA frame rate.
  • Optimisation of modulator and demodulator cover filters to minimise adjacent-channel interference into carrier and clock recovery circuits.
  • Investigation of adjacent channel multipath effects, which can cause severe problems during inter-burst guard time gaps on adjacent TDMA transponders. This work resulted in the ECS satellite channel spacing specifications being changed.
  • Optimisation of the pulse shaping filters for the Eutelsat ECS TDMA system.
  • Satellite IMUX and OMUX filter optimisation for the Eutelsat ECS TDMA system.
  • Investigation of anti hang-up techniques for burst-mode demodulators, including the use of quenched filters.
  • Study of carrier and clock recovery techniques for continuous-mode and burst-mode modems at 60 and 180 MBit/s.
  • Acceptance testing and performance evaluation of 60 and 180 MBit/s QPSK/TDMA modems and 2 kW Ku-Band HPAs.
Some Papers produced on the OTS and ECS Transmission Design
Some of the papers produced include :
  • Back-to-Back Performance of Pulse-Shaping Filters.
  • Effect of Satellite TWTA on Telephony Distortion.
  • Spectrum Spreading.
  • Determination of TWTA Saturation.
  • HPA Power Transfer Characteristics with a Modulated Carrier.
  • OTS and ECS Adjacent Channel Interference, Multipath and Distortion.
  • ECS Performance with Cosine Roll-Off Pulse Shaping Filters : Effect of Division of Power Law between Transmitter and Receiver.
  • ECS System : Optimum TWTA Operating Point for Different Pulse Shaping Filters.
  • Adjacent Channel Multipath in ECS.
  • Simulated E/No Values - Effect of Clock Phase offset and Demodulator Carrier Phase Offset.
  • In-Plant Acceptance Tests of High Speed (180 MBit/s) Digital Test Subsystem.
  • On-Site Acceptance Tests of High Speed (180 MBit/s) Digital Test Subsystem.
  • 60 MBit/s Station Loop Tests : Continuous Mode Performance.
  • Adjacent Channel Interference in the 60 MBit/s Digital Equipment.
  • Adjacent Channel Interference in the 180 MBit/s Digital Test Equipment.

Design of a Variable Data Rate High Speed Burst-mode QPSK Modem
The design of this modem was for a Government customer of Carrick Communications.
Design of a Hybrid TDMA system
Carrick Communications carried out the detailed design of a Hybrid TDMA system for a European PTT Administration.
Training Materials and Training for the INTELSAT 120 MBit/s TDM/DSI System

A large amount of work was carried out on the INTELSAT 120MBit/s TDMA/DSI system. See This Link for details.